Internal combustion engines require accurate timing of an ignition or fuel injection event with respect to piston position, in order to obtain maximum operating efficiency and output power with a given quantity of fuel with minimum emission of noxious components. Apparatus to determine the position of the piston in the cylinder of an internal combustion engine is therefore needed in order to determine the optimum ignition instant. This optimum ignition instant presupposes presence of a reference signal with respect to which the ignition instant can be computed in dependence on operating parameters of the engine, or operation parameters thereof, such as temperature, pressure (or, rather, vacuum) in the induction pipe, speed, composition of exhaust gases, and the like.
It has previously been proposed to couple a disk which has a single tooth thereon to the shaft of an internal combustion engine. An inductive transducer is in inductively coupled relationship to the tooth on the disk, to provide an output signal when the tooth passes the inductive transducer. A further disk, or sequence of teeth on the same disk, can be provided which induce in the transducer additional output signals to supply data from which the optimum ignition instant can be computed.
It has been found that providing a disk having a plurality of teeth within a predetermined range, coupled to the drive shaft on an internal combustion engine, causes difficulties. Such a disk must be made with extreme accuracy; manufacture thereof, particularly when it is intended to be used with multi-cylinder internal combustion engines is expensive and time-consuming.